How to join the output of 2 nested loops next to each other?

Question

So I'm currently working on a personal project and I made a program that prints out star patterns. On one of the star patterns I want this output:

Figure

*        *
**      **
***    ***
****  ****
**********

So I made one method print out this:

Figure 1

for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= i; j++) {
        System.out.print("*" + " ");
    }
    System.out.println("");
}

*
**
***
****
*****

And another method print out this:

Figure 2

for (int i = 0; i < n; i++) {
    for (int j = 2 * (n - i); j >= 0; j--) {
        System.out.print(" ");
    }
    for (int j = 0; j <= i; j++) {
        System.out.print("* ");
    }
    System.out.println();
}

    *
   **
  ***
 ****
*****

My question: How can I put the first method stars next to the other method stars?

This is what I got so far:

public static void printStarsVictory(int n) {
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= i; j++) {
            System.out.print("*" + " ");
        }
        System.out.println("");
    }
    for (int i = 0; i < n; i++) {
        for (int j = 2 * (n - i); j >= 0; j--) {
            System.out.print(" ");
        }
        for (int j = 0; j <= i; j++) {
            System.out.print("* ");
        }
        System.out.println();
    }
}

This is what is printing so far:

*
**
***
****
*****
    *
   **
  ***
 ****
*****

Any idea how to solve this?

Sash Sinha · Accepted Answer · 2020-11-18T17:28:39.800

I think you are on the right track you just need to combine your two programs into the inner for loop:

private static void printStarsVictory(int n) {
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j < n * 2; j++) {
            if (j <= i || j >= (n * 2 - i)) {
                System.out.print("*");
            } else {
                System.out.print(" ");
            }
        }
        System.out.println();
    }
}

Example Usage printStarsVictory(5):

*       *
**     **
***   ***
**** ****
*********

Example Usage printStarsVictory(12):

*                     *
**                   **
***                 ***
****               ****
*****             *****
******           ******
*******         *******
********       ********
*********     *********
**********   **********
*********** ***********
***********************

Vasia Zaretskyi · Answer 2 · 2020-11-18T17:18:42.717

1

Well, System.out.println() prints only to the next row, not to the right. The only way is to create a new algorithm. You should put everything into single loop.

// loop starts from 0 and user counts from 1, so we wil decrement it by 1
n--;

// this loops moves pointer vertically
for (int i = 0; i < n; i++) {

    // this loops moves pointer horisontally
    for (int j = 0; j < n*2; j++) {

        // here we choose what to print
        if (j <= i || j >= n*2-i) {
            System.out.print("*");
        } else System.out.print(" ");
    }
    System.out.println();
}

edited Nov 18 '20 at 17:18

answered Nov 18 '20 at 16:58

Vasia Zaretskyi

349
3
9

Your answer is lacking clarity. Can you please edit it and make it clear? Ex. Add Example, Show Code etc – Joseph Attia Nov 18 '20 at 17:00
now it should work better, I have also added some comments – Vasia Zaretskyi Nov 18 '20 at 17:19
Just looked at this for the first time... This does not produce the expected output for either an even or positive `n`. – Sash Sinha Nov 18 '20 at 18:03

score 1 · Answer 3 · answered Nov 18 '20 at 17:04

Each row has the increasing number of stars and decreasing number of spaces.

e.g. For n=5 first row has 2 stars at each side and 8 spaces.

At each iteration you can increase stars and decrease spaces and print them on the same line:

public static void printStarsVictory(int n) {

    int sp = n * 2 - 2; // number of spaces

    for (int i = 1; i <= n; i++) {
        printStars(i); // print stars on the left side
        int temp = sp;
        while (temp > 0) {
            System.out.print(" ");
            temp--;
        }
        printStars(i); // // print stars on the right side
        System.out.println(""); 
        sp -= 2; // decrease spaces on each side 
    }
}

public static void printStars(int i) {
    while(i>0) {
        System.out.print("*");
        i--;
    }
}

score 1 · Answer 4 · answered Nov 18 '20 at 17:14

Can you keep them in an array before printing to output:

public static void printStarsVictory(int n) {
    StringBuilder[] lines = new StringBuilder[n + 1];

    for (int i = 0; i < n; i++) {
        lines[i] = new StringBuilder();
        for (int j = 0; j <= i; j++) {
            lines[i].append("*" + " ");
        }

        for (int j = 2 * (n - i - 1); j > 0; j--) {
            lines[i].append(" ");
        }
    }

    for (int i = 0; i < n; i++) {
        for (int j = 2 * (n - i - 1); j > 0; j--) {
            lines[i].append(" ");
        }
        for (int j = 0; j <= i; j++) {
            lines[i].append("* ");
        }
    }

    for (StringBuilder line : lines) {
        System.out.println(line);
    }
}

score 0 · Answer 5 · 2021-03-25T20:33:04.533

You can visualize this figure as a matrix of numbers in a range: [-n, 0] inclusive vertically and [-n, n] inclusive horizontally, where each point is:

m[i][j] = Math.abs(i) - Math.abs(j);

If n = 4, then this matrix looks like this:

  0  1  2  3  4  3  2  1  0
 -1  0  1  2  3  2  1  0 -1
 -2 -1  0  1  2  1  0 -1 -2
 -3 -2 -1  0  1  0 -1 -2 -3
 -4 -3 -2 -1  0 -1 -2 -3 -4

Try it online!

int n = 4;
IntStream.rangeClosed(-n, 0)
        .map(Math::abs)
        .peek(i -> IntStream.rangeClosed(-n, n)
                .map(Math::abs)
                .mapToObj(j -> i > j ? "  " : "* ")
                .forEach(System.out::print))
        .forEach(i -> System.out.println());

Output:

*               * 
* *           * * 
* * *       * * * 
* * * *   * * * * 
* * * * * * * * *

^{See also: Making an hourglass using asterisks in java}

score 0 · Answer 6 · answered Jun 24 '21 at 10:26

Similar to this previous answer, you can use two nested for loops and one if else statement in the same way:

public static void main(String[] args) {
    int n = 9;
    for (int i = -n; i <= 0; i++) {
        for (int j = -n; j <= n; j++)
            if (Math.abs(i) <= Math.abs(j)
                    // in chessboard order
                    && (i + j) % 2 == 0
                    // vertical borders
                    || Math.abs(j) == n)
                System.out.print("*");
            else
                System.out.print(" ");
        System.out.println();
    }
}

Output:

*                 *
**               **
* *             * *
** *           * **
* * *         * * *
** * *       * * **
* * * *     * * * *
** * * *   * * * **
* * * * * * * * * *
** * * * * * * * **

^{See also:

• How to print a given diamond pattern in Java?

• Empty diamond shape with numbers}

How to join the output of 2 nested loops next to each other?

6 Answers6